Gazprom: Ukraine will owe $5.2 billion on June 7

A view of the Russian gas giant Gazprom's recently built Adler thermal power plant in the Russian Black Sea resort of Sochi.

Ukraine will owe Russia $5.2 billion for natural gas as of June 7 if it makes no payments by that date, the CEO of state-controlled Russian gas exporter Gazprom, Alexei Miller, said on Wednesday.

Gazprom says Ukraine now owes more than $3.5 billion, and has threatened to stop supplying the neighborliness former Soviet republic with gas if it fails to make a pre-payment for June supplies by June 2.